This invention finds particular utility in the field of read-only memory comprising magnetic recording media. An example is floppy disk media.
Read-only memory devices of this type can be used, for example, to stress-test disk drives in order to evaluate the drive's ability to read conventional floppy disks of the read-write variety. Another use of such a master disk is to evaluate how accurately the head of the disk drive is located. Since the master disk's data pattern is at a known position, if the drive's head does not provide an output signal which is within manufacturing specification, the drive is defective.
The prior art provides master disks using conventional media which is written in as accurate a manner as is possible. For example, a floppy disk, having a polyester film (Mylar by E. I. DuPont de Nemours & Co.) substrate which is coated with a continuous magnetizable layer, is placed in a master disk writer. This disk writer is constructed to produce as accurate a data track as possible, considering all of the dimensional tolerances, etc. which inevitably creep into such a disk writer. Uses to which such master disks are put are shown, for example, in U.S. Pat. No. 4,097,908, UK Pat. No. 1,533,778, and the IBM TECHNICAL DISCLOSURE BULLETINS of September 1973 (pages 1338-1340) and October 1977 (pages 1897-1901). These publications are incorporated herein by reference for the purpose of showing the types of master disk read-only data patterns which may be made by practicing the present invention. However, in its broadest aspects, the present invention is not to be limited to any particular data pattern.
As is readily apparent, the ability to reliably test or stress a disk drive, using a master disk, is only as good as the master disk itself is accurately written.
Background of the present invention is also found in the thin film memory arts, where photoresist and etching techniques are used to form selective, accurately located patterns. U.S. Pat. Nos. 3,677,843; 3,738,865 and 4,098,917 are exemplary.